416 INTRODUCTION TO EVOLUTION 



ing simultaneous change in two dimensions. Fig. 18.5 shows one of his most 

 famous examples. The figure at the right approximates the outline of a 

 huge marine sunfish of most unusual proportions. Almost circular in pro- 

 file, the fish seems to be mostly head, the relatively short body and tail fin 

 being excessively broad, vertically. A close relative is the fish shown at 



FIG. 18.5. Transformation of the body outline of a teleost fish, Diodon (left), to give 

 the outline of the sunfish, Orf/iagor/scus (right). The outline of Diodon was inscribed in 

 a framework of rectangular coordinates and the latter were then distorted in a regular 

 manner as indicated. (Redrawn from Thompson, On Growth and Form, Cambridge Uni- 

 versity Press, 1942.) 



the left, a creature of smaller size and more "usual" proportions, re- 

 sembling the presumed ancestor of the fantastic sunfish. If this outline of a 

 "normal" fish is inscribed in a grid of rectangular coordinates, as shown, 

 and then this system of coordinates is distorted in the regular way indicated 

 at the right, the result is the shape possessed by the weird sunfish. What 



